A “HFC refrigerant” such as nonflammable R410A has been conventionally used as refrigerant for a refrigeration cycle performed by an air-conditioning apparatus, which is one of refrigeration cycle apparatuses. Unlike a conventional “HCFC refrigerant” such as R22, this R410A has an ozone-depletion potential (hereinafter referred to as an “ODP”) of 0 (zero) and does not deplete an ozone layer, but has a high global warming potential (hereinafter referred to as a “GWP”).
Thus, as a part of prevention of global warming, it has been investigated to shift from a high-GWP HFC refrigerant such as R410A to a low-GWP refrigerant.
Candidates of such a low-GWP refrigerant include an HC refrigerant such as R290 (C3H8: propane) and R1270 (C3H6: propylene), which are natural refrigerants. Unlike a nonflammable R410A, the candidate refrigerants are extremely flammable, and thus, a caution is needed against refrigerant leakage.
Candidates of such a low-GWP refrigerant also include R32 (CH2F2: difluoromethane) having a GWP lower than that of R410A, as an HFC refrigerant having no double bonds of carbon in its composition.
Candidates of similar refrigerants include halogenated hydrocarbon, which is a type of an HFC refrigerant similar to R32 and has double bonds of carbon in its composition. Examples of halogenated hydrocarbon include HFO-1234yf (CF3CF═CH2: tetrafluoropropene) and HFO-1234ze (CF3—CH═CHF). To distinguish from an HFC refrigerant such as R32 having no double bonds of carbon in its composition, an HFC refrigerant having double bonds of carbon is often referred to as “HFO” using “O” that stands for olefin (unsaturated hydrocarbon having double bonds of carbon is called olefin).
Such a low-GWP HFC refrigerant (including an HFO refrigerant) is not as highly flammable as an HC refrigerant exemplified by R290 (C3H8: propane), which is a natural refrigerant, but unlike nonflammable R410A, has a flammability at a slightly flammable level. Thus, similarly to R290, a caution is needed against refrigerant leakage. Refrigerant having flammability, including refrigerants at a slightly flammable level, will be hereinafter referred to as “flammable refrigerant.”
In a case where flammable refrigerant leaks into an indoor living space (hereinafter referred to as a room or indoor), a refrigerant concentration in the room increases and may reach a flammable concentration. Specifically, in a slow leakage which may result from leakage refrigerant through a pinhole in a weld zone of pipes of a heat exchanger mounted in an indoor unit or from a joint portion of an extension pipe connecting the indoor unit to an outdoor unit, a flow rate of leakage is small and a flammable concentration is not reached. On the other hand, in a fast leakage which may result from a break of the extension pipe due to an external force or the of detachment of the joint to the extension pipe, a flow rate of leakage is high and a flammable concentration may be reached.
In view of this, to prevent refrigerant leakage from an indoor unit into a room, a split-type air-conditioning apparatus (see, for example, Patent Literature 1) is disclosed as follows. In this apparatus, the indoor unit is connected to an extension pipe by welding (hereinafter referred to as an “extension pipe weld zone”) without using a joint and a weld zone (hereinafter referred to as a “heat exchanger pipe weld zone”) between the extension pipe weld zone and a pipe of a heat exchanger is housed in a sealed casing. This configuration is intended to keep leaked refrigerant in the sealed casing even when refrigerant leaks in the extension pipe weld zone or the heat exchanger pipe weld zone.